Move plugins to manifest, pin Docker version, add Makefile

- Add plugins.txt listing all plugins for reproducible installs
- Add Makefile with setup/start/stop/install-plugins targets
- Remove user/plugins/ from git tracking
- Pin Docker image to 1.7.49.5-ls244

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/flex-objects/templates/flex/user-accounts/collection/default.html.twig

@@ -1,25 +0,0 @@
-{%- set request = grav.request -%}
-{%- set object_context = object ?? {} -%}
-{%- set object_layout = object_context.layout ?? ('list-' ~ layout) -%}
-{% if blacklist %}
-    {% set collection = collection.unselect(blacklist) %}
-{% endif %}
-
-<div id="flex-objects">
-    {% if title %}
-        <h2>{{ title|e }}</h2>
-    {% endif %}
-
-    {% if content %}
-        <div>{{ content|markdown }}</div>
-    {% endif %}
-
-    <ul class="list">
-        {% for object in collection %}
-            {% set link = request.uri ~ '/id:' ~ object.key %}
-            <li>
-                {% render object layout: object_layout with object_context|merge({link: link}) %}
-            </li>
-        {% endfor %}
-    </ul>
-</div>